Field of the Invention
The present invention relates to a cylinder head gasket in relation to a sealing technique, and more particularly to a cylinder head gasket provided with a leakage detecting function of a chain case side end portion. The cylinder head gasket according to the present invention is used in a three-surface sealing portion which is constructed by a combination of a cylinder block, a cylinder head and a chain case in an internal combustion engine.
Description of the Conventional Art
Conventionally, as shown in FIGS. 2 and 3, there has been known a cylinder head gasket 11 which is installed between a cylinder block 21 and a cylinder head 31 in an internal combustion engine and seals a three-surface sealing portion 51 constructed by a combination of the cylinder block 21, the cylinder head 31 and a chain case (a front cover) 41 (refer to Japanese Unexamined Patent Publication No. 2010-121662). Further, as an example of this kind of gasket, there is a structure in which a chain case side oil seal bead 13 is provided in a chain case side end portion in the gasket 11, as shown in comparative reference views in FIGS. 4 and 5.
The chain case side oil seal bead 13 is structured such as to seal the chain case 41 so as to prevent an oil flying in all directions within the chain case 41 from leaking to an external portion of the engine, and a seal bead line is disconnected in a gasket end portion, and is not formed as a closed loop, but is formed as an open loop shape which is open toward a side of the chain case.
In the meantime, a leak test has been universally executed before shipping conventionally in the cylinder head gasket. As a current testing method, pressurization is applied to an individual closed-loop seal bead by using a leak tester, and a quality guarantee is carried out by checking a leak amount.
However, since the testing method accompanies the pressurization, the testing method can be applied only to the closed-loop seal bead, and can not be applied to the open-loop chain case side oil seal bead. Accordingly, it is necessary to execute a visual check of an outer appearance in the open-loop chain case side oil seal bead. Further, since the visual check is a human operation, and a great dispersion is generated in a reference of determining good or bad according to a level of a viewer, an improvement thereof is required.